Voltage regulating apparatus



2 Sheets-Sheet 1 June 12, 1956 E. N. KATHER ETAL I VOLTAGE REGULATINGAPPARATUS Filed March 29, 1952 5R 6 Y mum 5 HA N 4 m M M .3 a WWW F A 4I fl 0 7 W IIIL 0 L a h w 2 2 a a A m m y P F Y Q A Y M mm au 5 June 12,1956 E. N. KATHER ET AL VOLTAGE REGULATING APPARATUS Filed. March 29,1952 2 Sheets-Sheet 2 MAGNE TIC FIELD DE/VS/ T Y B ,w A a a |||l||l|lllJfill' fl w u T G l. g s D D 8 m I m N I F a M W w m l m M E A g Frlllllllj/ a 55 s 0 w ANODE CURRENT I INVENTORS 5/2/0 NEV/N KATA/El?THOMAS A. o. GROSS;

BY AT ORNEV Ba 3b 3c MAGNET/C FIELD DENSITY B 2,750,555 Patented June12, 1956 VOLTAGE REGULATING APPARATUS Erich Nevin Kather and Thomas A.0. Gross, South LincohaMasn, a'sslgnors to Raytheon ManufacturingCompany, Newton, Mass, a corporation of Delaware Application March 29,1952, Serial No. 279,476 5 Claims. (Cl. 323-22) This invention relatesto a means for deriving a substantially constant voltage from a sourceof electrical energy which is subject to variations in voltage andcurrent and, more particularly, relates to an electron discharge devicehaving a magnetic field associated therewith for producing a constantvoltage.

Among the most widely used voltage regulators are cold cathodegas-filled diodes, such as neon glow discharge tubes. These tubes havecertain disadvantages which detract from their performance as voltageregulating devices. Such tubes have a relatively poor response totransients so that the output'voltage will not remain constant if thepower supply voltage varies rapidly. Furthermore, these regulator tubesare characterized by comparatively large hysteresis owing, principally,to the relative immobility of the heavy gas ions as compared withelectrons whose masses are extremely small; because of this hysteresis,the voltage drop across the tube will vary with the direction offluctuation in voltage and the response of the tube to rapidlyincreasing and decreasing voltage is relatively poor. Anotherdisadvantage of such tubes is that the voltage required to ignite theglow tube when the circuit is first energized is higher than the normaloperating terminal voltage. It is necessary, therefore, to

supply a voltage equal to or higher than the starting or,

ignition voltage, which, in conventional glow discharge voltageregulators, is approximately thirty per cent greater than the normaloperating voltage; in addition to the requirements for high sourcevoltages, the regulation of transients is poor when high-startingvoltages are re-,

quired.

An additional disadvantage of gas discharge regulators is that life isrelatively short because of absorption of gases by the electrodes. Sincegas pressure and gaseous content are voltage-determining parameters intubes of this type, an absorption of gas results in instability whichincreases as the tube ages. Finally, the voltage and ourrent range insuch tubes is severely limited. For example,

typical gaseous regulator tubes, such as tube type 0A3, are designed tooperate within a range of only approximately five milliamperes to thirtymilliamperes. These tubes will regulate at only one fixed value ofvoltage, such as 150 volts; such tubes, therefore, are inflexible. Wherethe voltage to be regulated is higher than approximately 150 volts,resort must be hadto two or more of such tubes in series. It is evident,therefore, that the number of tubes necessary for regulation of highvoltages becomes prohibitive.

Pursuant to this invention, the voltage regulator com-v prises a diodeelectron discharge device including an evacuated substantially gas-freeenvelope containing concentrically positioned cylindrical electrodes anda means for producing a magnetic field to control the current betweensaid electrodes. By making the strength of the magnetic field equal toor substantially equal to the cut-0E value corresponding to the value ofvoltage to be regulated, the electron discharge device has avoltage-current characteristic which is substantially flat over a verywide range of current. This device, ftherefore, serves as an excellentvoltage regulator over a wide current range.

The strength of the magnetic field may be readily varied, as by varyingthe current flow in an electromagnet surrounding said discharge device,to the cut-oif value corresponding to any voltage. In this way theregulator is capable of regulating satisfactorily over a wide range ofvoltages.

In the drawings:

Fig. l discloses an embodiment of the voltage regulator tube accordingto the invention;

Fig. 2 illustrates a modification or the field structure of the tube ofFig. 1;

Referring to Fig. i, one form of regulating device embodying the subjectinvention comprises an electron discharge tube ll having an evacuatedglass envelope 10, which may be a miniature envelope, such as the T5%envelope, from which substantially all of the gases have been removed.This tube may include a getter for insuring the absorption of whatevergaseous vapors may still remain inside the envelope after sealing. Acylindrical indirectly-heated thermionic cathode H is positioned withinenvelope it) with its longitudinal axis coincident with the longitudinalcenter line of said envelope. The cathode is supported by lead wire 12soldered at one end of the cathode, as shown in Fig.1. A conventionalheater is mounted inside cylindrical cathode Ill, the ends l3 and 13' ofsaid heaterbeing securely fastened to lead wires 14; and N, as shown inFig. l. A cylindrical anode 16 is concentrically positioned with respectto cathode 11 and is supported, by lead wires 15 and 15 solderedthereto. Mica spacers l7 and 17' serve to properly space the anode andcathode within said tube. These spacers have slits into which tabs 18 oncylindrical anode 116 are inserted. Cathode 11 is inserted in a circularaperture in the center of said spacers. The length of the cathode andanode is dependent in large part upon the dissipation required of thetube. The ratio of the anode radius to the cathode radius should begreater than 2.023. The lead wires are brought out to pins 19 extendingthrough a glass header seal externally of the tube base, as clearlyshown in Fig. l.

The tube is adapted to be inserted in a standard sevenprong miniaturesocket 2d fastened to a chassis or other support Ill by eyelets 22 orany'other appropriate fastening device. Surrounding the electrondischarge tube l is a hollow cylindrical permanent magnet 23 which maybe made of steel or any other. magnetic material having a highremanence. This magnet is adapted to provide an axial magnetic fieldparallel to the longitudinal axis of tube 1. Magnet 23 is secured to thechassis or support 21 by screws 24 or byany other fastening means whichwill mount the magnet in its correct position. The regulator tube 1 maybe quite small; for example, for 300 volts, a cathode 0.2 centimeter indiameter and an anode 0.5 centimeter in diameter can be used with afield of 550 gauss. v i

If it is desired to maintain constant a different value of voltageacross the tube 1, magnet 23 may readily be replaced by another magnetof diiierent field strength merely by removing screw 24 from the chassis21.

In Fig. 2, a modification of the magnet in Fig. l is kept constant.

shown. The field-producing means of Fig. 2 is an electromagnet 23 havinga core 24 upon which a winding 25 is wound. When weaker fields aresatisfactory, portion 24 may be a supporting spool or form made of anydesired material upon which coil 25 may be wound.

As is well known in the art, electrons traveling from cathode to anodein a diode having a magnetic field perpendicular to the electric fieldexisting between cathode and anode follow quasi-cycloidal paths in aplane normal to the magnetic field.

If no magnetic fields were present, the electrons would move directlyfrom the cathode to the surrounding anode, as shown in curve a of Fig.5. As the magnetic field is increased, the electrons proceed to theplate in a curved rather than a direct path, as shown in curve b of Fig.5. If the magnetic field is sufficiently strong, the electron orbitsmiss the anode completely and return to the cathode in an epicycloidalpath of relatively small diameter. This condition of zero current isillustrated by curve d of Fig. 5. At a critical value of field strength,the electron orbits just reach the anode before returning to thecathode, as shown in curve c of Fig. 1. This critical field is calledthe cut-off field.

From zero magnetic field to cut-off, the current in the tube issubstantially constant, provided the voltage is This substantiallyconstant value of current is determined by the space charge limitation.At

- cut-off the current drops from a substantially constant value to zeroand, for fields above cut-off, the current is substantially zero. Thevariation of current passed between the cylindrical diode at constantvoltage as a "function of the magnetic field is shown in Fig. 6. As thevoltage is progressively increased from En. to El: and thence to Be, itwill be seen from Fig. 6 that the current for a given magnetic fieldstrength B increases.

The variation of current in this diode with voltage at constant magneticfield is also of interest. The curves of Fig. may also be used toexplain the effect of voltage on current flow. Assuming a constantmagnetic field for small voltages, the electron orbits will all be bentaround by the magnetic field and will return to the cathode, as shown incurve at of Fig. 5. The current is therefore zero. As the voltagebetween anode and cathode increases, a critical or cut-off value isreached at which the electron orbits just reach the anode, as shown incurve c of Fig. 5.

The relationship between the magnetic field at cut-off Be and thevoltage Ec between cathode and anode, in terms of cathode and anoderadii re and n, respectively,

is given as e r, 5 9 a l -(z) where e is a charge on the electron and mis the electron mass.

The curve of voltage as a function of magnetic field at cut-off is aparabola, as shown in Fig. 7. The portion to the left of curve 40 is theregion of current flow, while the area to the right of said curve is acut-off region. If a constant voltage Eb is desired, the magnetic fieldis adjusted to a value Bb, as shown in curve 40 of Fig. 7, at whichcurrent just starts to flow. If the voltage is increased to Be, astronger field Be will be necessary to obtain the cut-off condition;similarly, the cut-ofi field for a voltage E. is reduced to a value Ba.For operation at or near cut-off, a current-voltage characteristic, asshown in Fig. 8, results. The group of curves shown in Fig. 8 representsthe variation of anode current of the electron discharge device 1 withanode voltage for different values of magnetic field intensity.Referring to curve 60, the lower and upper current limits for operationas a voltage regulator are shown as I1 and 1:, respectively. Eificientuse of this tube as a voltage at which the characteristic ceases to belinear) be at a minimum and that the change in voltageAE be small forlarge values of Al.

The actual cut-off voltage E0 is somewht lower than the theoretical orprojected cut-off voltage Ep- This results from various causes. Forinstance, it is impossible to the axis of the tube electrodes. Othercauses for the knee of the characteristic of Fig. 8 are divergence orfringing of the field at the ends of the electrode structure and thecollision of electrons of unequal velocity moving in different paths.These effects, however, are quite small and may be materially reduced byproper and careful design so that the knee 'of the characteristic, andconsequently I1, may be reduced. In Fig. 8, the curve 61 illustrates therelationship between the voltage and current when the cut-off magneticfield Be is higher than the value obtaining for curve 60, while curve 62illustrates the characteristic for lower values of cut-off magneticfield Be. The ratio for contemporary gaseous regulators, such'as thetube types 0A2, 0A3, 0R2, etc., is approximately five. Ratios of Al toI1 far in excess of present gaseous regulators may be obtained by use ofthe tube of the subject invention.

Referring to Fig. 3, the regulating device 1 is shown connected betweena power supply 50 and a load circuit 51 across whose terminals aconstant voltage is .desired. One terminal of power supply 50 isconnected by a lead 52 through a series resistor 55 to the anode 16 oftube 1. The negative terminal of power supply 50 is connected directlyto cathode ll of tube 1 via lead 53. Resistor 55 may, of course, beconnected to lead 53 instead of lead 52, if desired. The terminals ofload 51, across which a constant voltage is required, are connecteddirectly across the diode .1, as shown in Fig. 3. If the supply voltagedecreases, the regulator tube impedance increases, therebydecreasing theregulator tube current and the voltage drop across resistor 55.Likewise, an

shown in Fig. 4.

One terminal of coil 25 is connected to one end of a potentiometer 30. Asource of unidirectional current, such as a battery 31, is connectedacross the ends of said potentiometer. The cathode 11 and anode 14 areconnected to the terminals of power supply 50 in series with a resistor55, just as in Fig. 3. The load circuit 51 is connected directly acrosselectrodes 11 and 14 of tube 1, as in Fig. 3. A milliammeter 35,connected as shown in Fig. 3, serves to indicate substantially theattainment of the cut-off condition and the tube current during oper'ation.

If it is desired to change the regulated voltage from E. to a highervoltage Eb, as shown in Fig. 7, it is necessary, in order to maintain acondition of cut-off requisite for a fiat voltage-currentcharacteristic, that the field strength B be increased from Ba. to Be.By varying the potentiometer 30, the current flowing in coil 25 and,consequently, the magnetic field strength may be increased to thedesired value. If, for example, it is desired to maintain the voltageacross load 51 constant at voltage Eb instead of at El, the power supplyvoltage is boosted and the arm 29 of regulator requires that I! (thatis, the current at the point 7 potentiometer 30 is moved until meter 35,connected in the cathode-anode circuit of tube 1, indicates a currentsomewhere within the range of current 11 to Is, preferably at or nearthe midpoint of this range. The values I1 and I2 may be determined oncethe curve of anode voltage versus anode current of the magnetron hasbeen obtained. Such an adjustment permits operation over the linearportion of the anode voltage versus anode current curve of Fig. 8 forall values of power supply voltage ranging from the minimum to themaximum values which may be encountered during voltage deviations of thepower supply.

The magnetic-electron regulator tube according to the imention ottersseveral advantages over existing regulator tu es.

Provided the limitations of electron transit time are not exceeded, theresponse of the regulator tube to rapid fiuc-' tuations or transients isquite rapid. Since this tube is free of gas and the consequent slowlymoving ions, the tube has little or no' hysteresis. Because of the rapidresponse and absence of hysteresis the tube may be accommodated toapplications which cannot be handled satisfactorily by gaseous tubes.Among these applications are pulse clipping and peak regulation ofvoltage transients. This tube may be used as a shunt regulator of powersupply voltages to provide a greatly improved'atteriuation of voltageripple at high frequency, such as 400 cycles or higher.

This tube does not require ignition and therefore the need forhigh-source voltages is eliminated. Since the tube is free of gas, theproblem of absorption of gases by the tube structure is obviated and thevoltage-determining parameters remain substantially constant, therebyinsuring long life and stability of operation.

This tube may be designed to operate at less than 100 volts up to ashigh a voltage as desired. The range in current is limited only at thelower end where difliculty may be experienced in obtaining suitablecharacteristics in the microampere region.

Over at least some of the voltage-current regionsthe size of thisregulator may be made smaller than the present regulators. For example,a 5,000-volt regulator may have an anode diameter of only one centimeterand a cathode diameter of 0.25 centimeter and would require a field ofapproximately 1,000gauss, while the 300-volt tube would require only 550gauss for an anode diameter of 0.5 centimeter and a cathode'of 0.2centimeter.

This invention is not to be limited to the specific tube and circuitsshown and described. For example, the use of subminiature tubes ispossible over certain voltage ranges. The magnetic field structure maytake forms other than shown in the drawing, such as a winding enclosedwithin said tube envelope. It is also possible to make the envelopesthemselves of magnetic materials, thereby considerably rediicing thesize of the regulator. The resistor shown in Figs. 3 and 4 of thedrawings may be replaced by an impedance, such as a condenser or otherdesired circuit arrangements. It is also possible to connect two or moreregulator tubes in series to provide regulation at higher voltages.

What is claimed is:

1. A voltage regulating apparatus comprising an electron evacuateddischarge device including only an electron source comprising anelectron emitting electrode and an electron collecting electrode, meansassociated with said device for-producing an axial magnetic field, aresistor connected to one of said electrodes, a source of voltageapplied between said electrodes in series with said resistor, thestrength of said magnetic field being substantially equal to the cut-offvalue for the desired voltage to provide a substantially constantvoltage between said electrodes over a wide range of current andvoltage, and a load circuit across which said constant voltage isdesired connected across said electrodes.

2. A voltage regulating apparatus comprising an electron evacuateddischarge device including only an electron source comprising anelectron emitting electrode and an electron collecting electrode,electromagnetic means surrounding said discharge device and energized byan adjustable source of unidirectional control voltage for producing anaxial magnetic field, an impedance connected to one of said electrodes,a source of voltage applied between said electrodes in series with saidimpedance, the strength of said magnetic field being substantially equalto the cut-off value for the desired voltage to provide a substantiallyconstant voltage between said electrodes over a wide range of currentand voltage, and a load circuit across which said constant voltage isdesired connected across said electrodes.

3. A voltage regulating apparatus comprising an electron dischargedevice including only a cylindrical anode and a cathode concentricallyarranged in an evacuated enclosure, means surrounding said device forproducing an axial magnetic field, a resistor connected to one of saidelectrodes, a source of voltage applied between said anode and saidcathode in series with said resistor, the strength of said magneticfield being substantially equal to the cut-off value for the desiredvoltage to provide a substantially constant voltage between said anodeand said cathode over a wide range of current and voltage, and a loadcircuit across which said constant voltage is desired connected acrosssaid electrodes.

4. A voltage regulating apparatus comprising an electron dischargedevice including only a cylindrical anode and a cathode concentricallyarranged in an evacuated gas-free enclosure, means surrounding saiddevice for producing an axial magnetic field, a resistor connected toone of said electrodes, a source of voltage applied between said anodeand said cathode in series with said resistor, means for adjusting thestrength of said magnetic field substantially to the cut-off value forthe desired voltage to provide a substantially constant desired voltagebetween said anode and said cathode over a wide range of current andvoltage, and a load circuit across which said constant voltage isdesired connected across said electrodes.

5. A voltage regulating apparatus comprising an electron dischargedevice including only a cylindrical anode and a cathode concentricallyarranged in an evacuated gas-free enclosure, an impedance connected toone of said electrodes, a source of voltage applied between said anodeand said cathode in series with said impedance, an electromagnetincluding a coil surrounding said device for producing an axial magneticfield, means for variably energizing said coil to adjust the strength ofsaid magnetic field to the cut-ofi value for the desired voltage tothereby provide a substantially constant voltage between said anode andsaid cathode over a wide range of current and voltage, and a loadcircuit across which said constant voltage is desired connected acrosssaid electrodes.

References Cited in the file of .this patent I UNITED STATES PATENTS1,548,952 Mills Aug. 11, 1925 2,352,231 Stratton June 27, 1944 2,624,867Cobine Jan. 6, 1953 FOREIGN PATENTS 627,335 Germany Mar. 13, 1936

